I am in the process of buying a home and the inspection service offers mold inspections wherein they perform air and surface tests using an air pump, Zefon Air-O-Cells, swabs, and petri dishes.  These are then sent to a laboratory in 24 hours.  Are these relatively expensive tests?  Are they effective?-Karen, Massachusetts

            Routine testing for airborne and surface mold prior to a home purchase is not recommended.  Such testing can be quite expensive ($400 to $1500) depending on the extent of testing.  Laboratory analysis for each sample typically runs $35 to $50 apiece, and some consultants who perform such tests may charge you double that, reasoning that is a part of the service they provide.

            Let’s assume that 2 Air-O-Cells are collected, one indoors and outdoors, 2 swab samples indoors, and 2 petri dish samples (assuming these are not setting plates, as these are not recommended) indoors and out, the analytical costs may be anywhere from $400 - $800 with at least another couple of hundreds of dollars for the testing service. 

            Now what do you get from this?  Not very much.  The swab samples are not usually very interpretable and for that matter the air tests using the sampling and analytical methods commonly used.

            In most cases a good home inspector should be able to identify areas of a house that may have a mold infestation problem or factors that may increase the risk of mold infestation (wet site, settling cracks in brick veneer, water stains on walls, etc.).  If the visual inspection reveals factors that pose a potentially significant risk of mold infestation and exposure and one is concerned about such exposures, then purchase is not recommended.

            One conducts mold testing after one identifies a potential problem and then wishes to evaluate its significance.  Such testing should have specific objectives,  that is (1) to identify whether a building-wide problem exists or a more localized one, and (2) to determine how high mold levels and what mold types are present.

            In most cases swab sampling does not reveal much about whether a mold problem exists or not because too few samples are collected and it is difficult to interpret their meaning.

            Air sampling is also problematic.  Too often only a few samples are collected using a single collection procedure.  Assuming test results are accurate (and in many cases they are not likely to be), they may be too few results to be interpretable.  For air testing to provide results that can be interpreted, mold inspectors should collect a minimum of three indoor samples with an Andersen-type sampler with an additional one outdoors.  An additional three samples should be collected with a total mold spore sampler (like the Air-O-Cell) with an additional one outdoors.  The latter should always be counted at 1000X magnification to minimize the likelihood of undercounts. 

            As you can see such testing requires a minimum of 8 samples and of course is likely to cost around $1000. 

February 6, 2004

Indoor Environmental Quality (2000), Thad Godish Ph.D., C.I.H

Direct E-mail 00tjgodish@bsu.edu